[The author sent this information on the AMIA listserv (AMIA-L@LSV.UKY.EDU) last December, in response to a query by James Hoagland: "Are there any studies showing that barium ferrite tape will last longer than other tapes?" It is reprinted with permission.]
There are a number of things that affect the aging of tape. Hydrolytic breakdown of the binder is certainly the most common and most evident. From a practical point of view, binder stability is the key issue on how long a tape will last.
The type of recording pigment (the metallic particle that actually holds the magnetic signal) usually has very little effect on binder stability. A new stability issue has, however, been introduced: the MP (metal particle) recording pigments being used in virtually all new tape formats are unstable. To put it simply, MP pigments are highly susceptible to oxidation: they rust! These particles are so unstable that they require "passivating." This process consists of coating the particles with a thin ceramic "armor" to isolate them from the environment. The single coating initially used was found to be inadequate to protect the particles and now most particles receive at least two coatings.
An accelerated aging study done in 1993 predicts that the more modern passivating processes will protect the particles from "loss of magnetism due to oxidation and humidity" sufficiently to limit signal loss to 2db or less over a 96-year period of time. It remains to be seen how well such accelerated testing actually reflects "real-life" results.
The MP recording pigments are being used because they provide a magnetic recording medium significantly more efficient than the old "oxide" formulations. If the passivating coating does protect the pigments for 96-plus years, current trends concerning frequent migration to ever-newer formats may make the oxidation question moot for many archives. On the other hand, our extensive experience with disaster recovery clearly shows that the MP tape formulations are extremely subject to catastrophic failure when exposed to flood conditions. When MP tapes are submerged or come into direct contact with water, it is not uncommon for the passivating coating to fail to protect the recording pigments. This results in particle oxidation and may set up a "cascade" effect that destroys portions of the tape.
The "archival" claim for barium ferrite tapes deals with the barium ferrite recording pigment, not the binder. Barium ferrite does not rust the way MP pigments do. This doesn't require a lot of testing: it's a matter of simple chemistry. Is it relevant? That's up to you. IF the accelerated testing done on MP tapes reflects reality (not very likely) and IF you migrate your MP tapes before they oxidize and IF you don't get your MP tapes wet, there shouldn't be a lot of problems.
It seems counterintuitive to migrate archival recordings to new formats that have more inherently unstable elements than the older originals: both the binder and the new recording pigments are now unstable. On the other hand, while barium ferrite recording pigments may be more stable than MP, there remains the ever important question of the binder. Major manufacturers have developed "functional resins" and binder mixes that claim higher concentrations of long-chain polymers in an attempt to retard binder breakdown. Are these advances incorporated into the binder matrix of the barium ferrite tapes? It's a tough call. As we all know, no manufacturer will release complete specifications on their proprietary binder formulations.